Tandem axle vehicle suspension



L. .A. BOTKIN TANDEM VEHICLE SUSPENSION Feb. 24, 1959 5 Sheets-Sheet 2 Filed Jan. 15, 1957 40 Mllllhh, 40

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Feb. 24, 1959 LffBoTKlN TANDEM AXLE VEHICLE: SUSPENSION 5 Sheets-Sheet 3 Filed Jan. 15, -195'? n.. 0 w ,..-s....mw.....|.....w. 1 1

m4/renee .4. 507%?? Feb. 24, 1959 L. A. BOTKIN TANDEM AXLE VEHICLE SUSPENSION 5 Sheets-Sheet 4 Filed Jan. l5, 1957 INVENTOR.

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Feb. 24, 1959 L, A B01-Km 2,874,973

TANDEM AXLE VEHICLE SUSPENSION Filed JamI 15, 1957 Sheets-Sheet 5 v INVENTOR. l aw/few@ 5025607 www A TTORNEK ln'the accompanying drawings which form a United States Patent' O TANDEM AXLE VEHICLE SUSPENSION 1 Lawrence A. Botkin, Kansas City, Mo., asslgnor to `Butler Manufacturing Company, a corporation of Missouri Application January 15, 1957, Serial No. 634,279 7 claims. (cl, 28o-104.5)

This invention relates to multiple wheel vehicles and refers more particularly to an improved means for coni necting tadem axles with the vehicle. I

Heretofore considerable difficulty has been experienced in obtaining a suitable suspension arrangement for trailers or vehicles provided withtandem axles. Included among when the vehicle passes over obstructions and is traveling on rough roads; scuing of the tires and `consequent uneven wear resulting from turning of the unit; dogwalking of the trailer on crowned roadways; uneven distribution of brake draft and torque reactions to the mounting assembly; and` failure of or necessity of providing heavy suspension springs due to forcing ithem to absorb side and braking forces. t e

It is a primary object of the present invention to provide a tandem axle mounting for vehicles in which the foregoing problems are eliminated. It is a featureof my in-` vention that Ihave been able to provide a spring suspension for supporting a trailer on tandem axles in which the springs are not required to absorb either side or brakthese diiculties are uneven load distribution to the wheels ingforces; in which the axles are maintained,` during' and are, as a matter of fact, urged into `tracking position.

Another object of my invention is the provision of a tandem axle mounting in which independent articulation of the axles during both straight line travel and turning is permitted, thus `maintaining relatively even distribution of the load on the wheels even though the turn maneuver f is taking place on rough and uneven terrain.

A further objectof the invention is to provide a tandem axle mounting in which the arrangement and manner of connecting the axles is such that the vehiclewill tend to recover from a skid automatically. i i Still another object of the invention is toprovide a tandem axle mounting in which the brake torque reactions are utilized to increase the eifective braking forces exerted by the.wheel. Stated otherwise, it is an object of this invention to provide a tandem axle mounting in which the brake torque reaction is utilized to`cause the trailer to increase the Contact pressureof the wheels with the roadway above that supplied by` the weight of the trailer alone.

Other objects of the invention are to provide improved means for connecting the axles with the frame; to provide a simple and improved spring suspension between the tandem axles andvehicle; and to provide animprov'ed tandem axle assembly in which parts replacement and re pair can be accomplished with ease and facility.` Afea'- ture of the invention resides in the ready interchangeability of the various parts, thus reducin'gsthe first cost and subsequent maintenance to a considerable extent.

Otherand further objects of the invention together with the features of novelty appurtenant v thereto twill; appear during the course of the `#following description. t f

prr or Patented Feb.: 24, 19H59 d i the specification and are to be read in conjunctiontherewith, and in which like reference numerals indicate like parts inthe various views:

Fig. lis a top plan view of a portion of a typical trailer embodying the features of the invention, parts being broken away for purposes of illustration and to indicate length; 1

Fig. 2 is a view taken along the line 2 2 of Fig. 1 in the direction of the arrows, parts again Vbroken awayfor purposes of illustration; i i i Fig. 3 is a view taken along the line 3--3 of Fig. 2 in the direction of the arrows; t

Fig. 4 is an enlarged view through one beam endsupport, the view being taken generally along the line 4--4 of Fig. 2 inthe direction of the arrows;

FigxS is a view taken along the line 5--5 the direction of the arrows;

Fig. 6 is an enlarged sectional view taken along the line 6- -6 of Fig. 1 in the directionof the arrows;

Fig. 7 is a view taken along line 7-71of Fig. 6in the direction of the arrows; i

Fig. 8 is an enlarged sectional view taken along the line 8-8 of Fig. 1 in the direction of the arrows;

Fig. 9 is a sectional view taken along the line 9--9 of Fig. 8 in the direction of the arrows; t t

Fig. 10 is asectional view taken along the line 10-10 of Fig. 8 in the direction ofthe arrows;

Fig. l1 is a perspective view of the central portion of :one of the beams with the circular slide bearing being .shownin exploded relation with respect to the beam;

Fig. l2 is a schematic top plan view of a trailer embodying the invention, the central portion of the trailer frame being broken away and the bearings: being shown in section; i

Fig. 13 is a view similar to Fig. 12` but showing the attitude `of the wheels and axles relative the frame during la turn maneuver; Y

Fig. `14 is a side view of the trailer and suspension illustrating the operation of the unit in passing over bumps or crowns, the wheels on the near side having been removed for purposes of illustration; and

of Fig. 4 is Fig. l5 is a schematic rear end view of the unit illus trating the freedom of vertical articulation of the wheels and axles in moving over irregular terrain.

In lmy invention I provide tandem axles which are connected with the vehicle independently of one another, each axle being universally pivoted through suitable draft means tothe frame of the vehicle. Spanning the axles are beam members which are so mounted with respect to the axles and frame as to absorb all side-nforcesand -transrnit them directly to the frame notwithstanding the fact that the frame is supported on the beam byspring means. The beam connection with the axles is such that independent angular movement of the axles is made possible, thus permitting free tracking of the' wheels during turn maneuvers as is illustrated generally in. Fig. 13. The mounting of the axles is also such thatthey are adapted `for relative vertical movement with respect to one another while maintaining the trailer level as shown in Fig. 14 and can be tilted in opposite directions with respect to the longitudinal center line of the trailer while maintaining the trailer frame substantially level, as illustrated generally in Fig. 15.

Referring now to Figs. 1, 2 and 3, the trailer chassis or frame is represented by the spaced longitudinal frame members 20 and. 21, which are preferably generally Z-shaped in cross section as shown in Fig. 3. IThe frame members 20 and `21 are rigidly connected with one another by suitablecross beams A(such as shown at ZZin Fig; 3) to forma rigid frame structure. It will be understood that the rear portion Vonly, of` the` trailerus shown, and that the front of the trailer is adapted to be (not shown).

Located beneath the trailer chassis and supporting same in a manner later to kbe described are a pair `of tandem {txlesconsisting of a lfrontaxle 23 and "a rear' axle 2`4."`Rotatably mounted atthe ends of front axle 23gare front wheels 25, and on'rear axle `24 rear wheels 26,."-The axles 123' and 24 are each independently connected jwith the `trailer chassis `by a `draft arrangement4 which in the case of'front axle 23 includes the converg'f ing draw bars 27 and in the case of the rear axle`24, similar draw vbars 28. The draw bars 27 and 28 extend forwardly' of 'their respective axles, beingrsccured at their rearward ends to the axles and converging toward, apair of draft bearings -29 lpositioned respectively aheadi of the front and rear axles.

The two' draft bearings 29 for the front andr rear axles 'are lidentical in construction and are' detailed 'in Figs. 6 and 7. It V*' will-"be noted that'each bearing is secured directly to the trailer chassis by a depending sup port structure which includes a -pair of downwardly con-- verging struts 30. The struts 30 each have theirupper ends secured to `th'echassis frame members 2.0 and 21 and-.fthe struts in each pair converge downwardly, their lower ends being welded or otherwise securedto a rearward Vextension 29a on the bearing 29 associated therewith.

'Referring again to Figs. 6 and 7, the main vbody of each bearing structure comprises a generally cylindrical split annular housing, the separate halves of whichV are bolted together by "bolts 31. The inside surface of the housing forms a spherical socket within which is rotat- .ably'supportedv a centrally apertured ball member 32 which maybe composed of nylon or any'other suitable -materalL' Extending centrally through `the 'aperture in 'ball member 32 is a threaded shaft 33 of somewhat smallerdiameter than the bore of the ball aperture. "A pair of internally threaded sleeves 34 are threaded onto the shaft 33 and extend into the bore of the ball. Sleeves: 34 are provided with annularflanges 34a which are formed to engage the ball around the margins of the opposite ends of the aperture.V Lock nuts 35 abut the sleeves 34 outside the ball to prevent. accidental turning thereof. yIt will 4'be evident that'the sleeves 34 serve to firmly secure the ball to the shaft V33.

The draw bars 27 and 28 are secured to the shafts `33.1f theirrespective bearings 29 by spaced parallel extensions 27a or 28a on the forward ends of the draw bars which lie on opposite sides of the ball element and are/apertured to t over shaft 33. The extensions are retained axiallyon the shaft between the lock' nuts 35 andretainernuts 36 threaded onto the outer ends of the shaft. lt"will be-understood, of course, that'while Pigs. 6 and `7 :show the details of the `bearing to Awhich draw -bars 128 are connected, the same arrangementisem .plyed'or connecting draw bars l27 tothe `'frontbearing' 29.

lult, will vbe evidentthat :the bearings 29 provide a uni- :versal pivot 'through which theaxl'es23 and 24 are .connected to -the trailer frame. Thus, the axles 23 and 124 are free to =tilt with respect to the longitudinal center -line .of the-trailer; to rise and fall about the axis of their -respective'sh'afts 33; and to swingabout a vertical axis lthrough the center ofthe draftv bearing associated there with. :It fshould 'be noted at this point that preferably -the1spa'cin`gif the bearings`29 ahead of theirassociated axles 23 or 24 is the same in each easel The weight of the' trailer chassis is carried in a fashion later' to :be described .on a pair of -similar rbeams 37 which preferablylhavecentral portions tapering toward '.thecopps'iteiends and -terrninatin'g'in -a forward cylindricalA extension 37a and a rear cylindrical extension`37'b. ,lhe'beams 37 are'located on opposite sidesof the trailer frame, Ybeing aligned `.generally with frame members 20 :aindlfand` are Ydisposed therebelow. To conserve weight,

connected with any vsuitable draft means such as a truck i jpreferably beams 37 are of a hollow construction as v'shown on --the v-right hand *side of Fig. v8. The beams ,extend transversely between the axles 23 and 24 with the .extensions or end portions 37a and 37b preferably over- Ilying the axle structure where they are received in special `supporting members 38 aixed to the respective axles.

The four supportingmembers 38 are basically identical in construction, eachk consisting (as shown in Figs. -4 and 5) of a housinghaving two `halves secured together :and forminga socket having a spherical portion retain- :ing therein a universally rotatable ball element 39.v The housings are welded-or otherwise firmly secured to the top of the respective axles. `Extending.centrally through 'each ball element 39 is a central bore within which are :slidably received -the cylindrical endportions 37a and .37b of the beams. As will be evident from Fig. 5, the

`-end portion of the beams are long enough to provide for llimited axial'movement of each extension relative to its ball'. Av-shoulder 37e is provided at the junction of the beam and extension Vto limitfrelative movement in Aone Idirection and a stop collar or ange 37d is Y,securedto the free end of each extension to limit movement in the opposite direction yTheV beams Vandvextensions are given dimensions such that when the axles 23 and 24 are -aparallel, the mid-point of the extensions 37a and '37b of .the beam substantially coincide lwith the centers of the ball elementvs39. 'Thus it `will be seen that the beams 37 .are lirmly supported'at each end on the front and rear axles, provision, however, being made through the support elements 38 for relativemovernent of the axles axially of the extensions' and also for relativeV angular movement in any direction. 7 Mounted on top of the respectivev beam supportrnem- `bers' 38 are stop plates 'P which, during articulation of the beams and axles, cooperate'pwith resilient bumpers B to limit the "maximum-movement ofthe axles relative to the-frame. The bumpersB are secured to and depend from the nunderside of frame members 20 'and 21.' On the forward plate members P, there are provided Vupstanding stop anges S arranged to engage the sides 0f the frame members 21 and 20l to limit the maximum turning angle, as will laterV become more apparent. l

Theload of .the trailer chassis is transmitted to the wheels through the "beams 37, the chassis being yieldably supported on the beams. In the preferred construction, each beam 37 has'surmounted thereon at its'midsection a pair of helical compression springs 40 which provide the yieldablel support for the chassis. The lower ends of springs 40- are `received in a pan-like retainer 41 which is provided with a central raised portion 41a forming a concavity in the underside within which `fits-a corresponding .boss 42 (seeFig. 1l) formed onthe'to'p ofthe beam."" l`he"cooperation between the boss 42 and concave undersideV of the raised vportion 41a serves to index the retainer 41 inV proper position on'top lof the beam and prevent the 'retainer'from departing from ythis position during use.` Y l' 4 :The frame members 20 and 21 of the trailer chassis are seated on the upper ends of springs 40 through the provision of extension plates 43 Fig. 8) which are welded orhotherwise rmly secured to the respective frame. membersV and extend' outwardly to overlie and contact thevupper ends of the springs.V The extending portionsof each plate 43 are ingturn'reinforc'ed against -bending Aby means of gussets 44 which are securedv to the adjacent side portions` of the Vframe" members" andtops of the plates y4s, 'preferably by Werding.

-One of the important features vof my invention resides in 'the factthat 'the beams 31 are universa'uy pivetedfat their longitudinal'rnidpoints to the frame by a connecting means'which Ypermits also limited up and `*down movement ofthe beanisrelativeto the frame; the pivot for each beam 'shifting alongv with the beam so that the 'universal pivot characteristicris present regardless of the vertical position f thev beams with respect to :the vfraint':

mid-section of each beam 37 is disposed between a pair of spaced vertical guide members comprising an inner guide member 45 and an outer guide member 46. The pairs of guide members 45 and 46 depend respectively from the trailer frame members 20 and 21, the inner guide member including an upright channel member 45a welded at its upper end to the trailer frame and the outer guide member including a similar channel 46a. The lower end of the outer channel 46a is secured to and supported on the outer end of` a cross member 48 which is rigidly secured at its inner end to the lower end of the inner channel 45a. The upper end of the outer channel 46a is supported bya tie brace 48a which is secured to and extends downwardly from the edge of plate 43. The lower end of tie brace 48a is secured to the upper end ofthe channel 46a wise.

As is believed evident from the drawings, channels 45a and 46a are oriented with their lianges in vertical planes confronting the sides of the beams 37; Fitting within the channels and coterminous therewith, and forming the beamconfronting portions of guide members 45 and 46, are slide members 45b and 46b. Each of the members 45b and 46b is provided onits beam confronting face with a vertically elongated trough, semicircular in cross section, which extendsfrom the top to the bottom thereof. Shims 49 may be provided between the` webs ofchannels 45a and` 46a and'their respective slide members 45b `and 46bto accurately control-the depth to which the slidemembers seat in the channels. The slides are retained axially withinl the channels vby flangedover lips 45d and 46d`at their upper ends and by the cross members 48 at the lower ends. The slide members 45h and 46b may be of hollow construction to permit slight deformation'for a purpose later to be described.

As has previously been mentioned, the beams 37 are in each case disposed between'their respective guide v members 45 and 46. Extending from each side of the beams and connected therewith in a manner later to be described is a bearing member 50 which is generally rectangular in plan, the bearing in each case being provided with a concave semi-cylindrical outer face 50a which is slidably received in the trough of the adjacent slide 45b or 46b. Thecurvature of the convex faces of bearings 50 and the troughs in slides 45b and 46b is the same. To'mount the bearing members 50` on beams 37, each beam is provided on its opposite sides with a cylindrical boss 51. The inner faces of bearings 50 are provided with corresponding cylindrical recesses which meet with the boses 51 to rotatably position the bearing members on the beams. A

Due to the cooperative relationship established between the bearing members 5,0 and the troughs of slides 46b and 45b`, the beams are universally pivoted to the frame while stillbeing capable'of up and down movement relative thereto.` Rotation `of the beam about the axis of bosses 51 is provided by the rotatable connection of the bearing members 50 therewith. As shown in thebroken lines in Fig. l the beamis also adapted to move about a vertical `axis throughthe center thereof, the bearing surfaces in this case being the slidably contacting convex and concave faces of the slides 46b, 45b and ofbearing members 50.` Since the vertical axis intersects the axis of bosses 51, universal pivoting of the beam relative to the guide members 45 and 46 (and hence the trailer frame itself) is provided.

The operation of the suspension assembly may be best understood by referring to Figs. 12-15, inclusive. In Fig. 12, the trailer is shown as moving forward in a straight line. The `front and `rear axles 23 and 24 are drawn with the trailer through the thrust connection by welding or othermaintain the wheels in a centralized condition under provided' by draw bars27 and 28 which are universally `pivoted to the frame through the draft bearings Z9. The

"wheels, for example, Aas may be occasioned bythe existence of highvcross wind loads on thesuperstructure (not shown) or when the trailer is ytraveling on a transversely inclined surface such as lis vpresented by roadways crowned in-the center for drainage. In either of these cases a resultant lateral force F (see Fig. l2) tending to force the wheelstransversely with respect to the chassis is created and tends to swing the wheels out of line. .In my invention, however, the beams 37 firmly (resist any tendency of the wheels to thusA depart from their`v centralized position since they` are. confined against any lateralmovement by their respective pairs of guide members 45 and 46. The side forces F are transmitted to the members 38, through the members 38 to the beams 37, and throughthe beams to the guide members 45 and 46 which, as previously described, are secured directly to the frame. By so confining the beams at theircenters against lateral movement the springs 40 are in no way required to resist Ithe side loads. Not only does this `facilitate the use of coil rather than leaf springs, but it also obviates the `'necessitytn giving the springs .any structural strength` other than the strength necessary to resist the compressive ,loads imposed thereon by the frame.` r t f Despite the operation of the suspension assembly to the circumstances seti` forth above,` the arrangement is such `that during a `change in direction of :travel of the vehicle the front and rear` wheels are capable of reorienting themselves so that the wheel ,planes are tangent to a radius line drawn from the turn center. This conditionis illustrated in Fig. 13 of the drawings. In the geometry of this gure Xindicates the imaginary center of the ground contact points of the wheels, this being what may be considered` the center of resistance to turning of the ltrailer whenthe turning moment is applied. The guide members 45 and 46 are so located that the point X lies in a vertical plane passing through the centers thereof. v The centerof the turnfor the trailer suspension assembly is located at C,` and R represents a radius from turn center C passingg ,through` point X and the; centers of the pairs of guides 45-and 46.` A

As the trailer moves into the Yturn the lateral move ment of the trailer frame displaces the forwardfdraft bearing, inwardly toward the turn center causing the front axle 23 to assume an angle with respect to the frame such that thefront wheels are tangent to a radius R1 from turn centerC. The. forwardends 37a of beams 37 move laterally with the axle 23 andthe axle assumes an acute anglewith the beams. `The, sliding connection of the beam extensions 37a with `theball elements `39 in the ball and socket members 38, and the rotatability of the ball within the sockets,` permits the necessary movement for the front `wheels to adjust. to the arcof the turn. The rear wheels will also `adjust to the arc of the turn through the provision of the universal pivot provided by the rear draft `bearing 29 and the sliding` and universal pivot` connection of the rearbeam extensions 37b with the rear axle 24 through ball and socket members 38.

The .beams 37 beinglixed laterally between guides` 45 and 46 (but pivoted therein in a horizontal. plane) insures that the angular movement of rear axle 24` with respect to the trailer will be equal to that of the front axlev 23, thus bringing the rear wheels into a position where' they are tangentxto a1-.radius :Rfrom .thesturn center C and Venting :them from ,assuming any other position. .It

el! agvill-thusbe,evident-that in ,ag-turnof any radius BD10 .guidemembers'45.and-.46 without `affecting the angular `vposition of :the vaxles 23vandg24xrelative to the frame.

The turn...characteristics .'ofzthe :vehicle arelikewise lun- ;aiectedzby changingLgroundzcontours in thetpaths of the wheels. As :will belnoted-:from Figs. i14 Vand :.15 the front :and rear axles are. capable of :independent :vertical and .angular .movementsrelative ;to.oneiano.ther. This-is Adue to the,independentuniversal'pivoting .of -the axles to the frame through thedraftbearings 29; tothe sliding and runiversally'pivotalfconnectirmfof thebeam ends 37a and ,37b `with :the axles; andY to ttheluniversal :pivoting of beams 37.fin.the guide membersASl-and 4'6. EvenV though v.the axles 23 and.24;may be inthe .turn'position .illustrated in Eig. ,13, Athe twheels :arehfree to adjustto changing ground contours, the -limits :being :defined by theV stop :plates EP vandbnmpers B previously described.. A:Of course, it-will be evident lthattheadaptation of the wheels to -changng Vground Vcontours"islobtained :in straight .line :travel aswwellaisduring turns. A

As is believed evident from the showing of Fig. '15, AAat -a'n'y time that the .axles 23' a'n'd'24 vare moved iout of parallelism, fthereysaislght pulling in of the lbeam lends toward pnetanother, this 'being due tothe fact that v:guides 45' and46' maintainv thecente'rsof the beams at a fixed lspacing-wliletheends ofthe beamsare carried onthe axles fandlm'ove Vabout ahypothetical center which is approximately at the' midpoint of the axles.' However, `the Ainherent fgivei in thebearns and lin ftlie sliding connection between Vthebea'ms and 'ther guidesV 45 and 46 has ybeen found more than'- enough topermitthe axlesto movev freelyin thedirections described without binding `at the sliding connections, whether for the beams or axles` If4 there appearsgtoberany undesirable binding, 'the slides 45h and 4 6br can be `made of resilient sheet metal vbent to vthetformgshown and described, thus to provide for a slight lateraliriovement of 'the beams 37 under theconditionsls'et forth,

It is a particularly 'valuable feature of invention :that the angular vertical 'movement of the Vaxles 23 and 24 is obtained without affecting `to any `great degree the Qflevelrposition offthfe Vtrailer.frainet This isdu'e'primarily jto tthe factthat thepoints fof support for the frame '(the springs 4.0.) are centered onfth'e midpoints o f beams 37 Vwhich move verticallyfonly alimited distance under any rzonditionof. operation. By vir-tueof the equidistant spacmg ofthe V,midpoints of the beams .37. between axles 23 and 2 4, a lift o f twelve inches iat; the Vvfront wheels will vvresult 4in only sixinch lift-atthe center Vof the beam and hence .only -a lift .ofa maximum of `sixinches of the frame.assumingthat:theli-ft iis Iso V'gradual that it would not .be I2 1bsorbe'c`l'fin-the `inertia `of the trailer `and com.- `pressive displacement of springs 38. Thus it will be seen 'that-under averagefconditions ofroughness ,of 4ground vconto-urffthe trailer will remain substantially level despite marked articulation of theaxles and beams, n

Y Another point which L"should :benoted is that =the'articulation of Athe axles illustrated in Figs. 14 and 15 results in, '21. llnifotm' 'distribution 'olf the .trailer .load 'to vall tour ofthe dualwheelassembliest lhisistrue SolQHgaS the 8 reunir ,'.l21e.1,imi,tS.-Qf.-n1orement cf thesbeamends :in their ball and tsslsetficintstfare.nottreached- Due to theconnecting of thekaxles 23 and 24 through forwardly located draft bearings 29, the application yof braking forces to the wheels isjabsorbed in the Vdraw bars 27 and `28 `and the draft bearings rather than .in` the articulating members .This is of `value in maintaining freedom ofmovement at the ball and socket connections 38. Furthermore, the independent absorption of the torque reaction at each axle prevents what is familiarly known as crow hopping of the vehicle when the brakes 4are applied.

While the description of the operation of my invention has been in connection with a trailer suspension in which the .wheels are capable of tracking on turns, it will be vunderstood that the independent up and down movement ofthe axles and their articulation in what-may be called a substantially vertical p lane as s hown yin Fig. 15 is independent of the free vtracking feature. l.In other words, the wheels have the ability to follow the ground contours when `the axles l23 and 24 remain in a vertical `plane normal to the `center line-of the trailer as shown y in Fig. 12. The only thing necessary to the varticulation asshown inFig. 15 is thaty the draft bearings provide for pivoting of the draw bars l27 `and 2,8.about van axis parallel with the centerline of the vehicle and anaxis transversetto the center line and/parallel with the wheels. The sliding and universally -pivotalconnection of the beams 37 with' the axles permits lfreie movement thereof to Ythe extent necessary to obtain the result desired.

From the foregoing it will be seen that this invention is one well adapted to attain all .o f the ends and objects lhereinabove set forth together with other advantages v'which are obvious andwhich are inherent to .the structure.

It Vwill be understood that certain featuresand subcombinations areof utility and maybe .employed without reference to other features and subcombinations. vThis is contemplated by and is Vwithin the scope of the claims.

s many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood `that all matterV herein set forth or shownin the accompanyingdrawings `is to be interpreted as `illustrative and notin a limiting sense.

Having thus described my invention, l claim:

l. In a tandem trailer assembly, .an elongate frame, two tandem axles spaced longitudinally of said frame and providing a forward and a rear axle, two pairs of wheels, one pair on each axle, a draft tongue for each axle extending forwardly thereof, means universally pivoting the forward end of each draft tongue to said frame `to provide for independent angular movement of the axles relative toone another, a pair of spaced forearidaftbeams spanning said axles, means universally pivoting the end portions of said bearnsto the. respective axles, said means constructed and arranged to permit movement of said end portions relative to said axles in a direction transverse to said axles, two pairs of spaced guide members, one on each side Yof said frame, the respective guide members extending downwardly 'on opposite sides of the respective beams whereby each beam is disposed between a pair of said guide members, means forming with said guide members a universal pivotfor each beam, said means being constructed and arranged to permit upward anddownward movement of said pivotrelative to saidguide memberspand yieldablemeans interposedbetween said frame'and beams andjsnpportin'g said frame thereon.

7.2..;In atandem trailer assembly, anrelpngate frame, two tandem axles spacedlongitudin'ally of s aidframeand providing aforward and a rearaxle, twol pairs of wheels, .one pair on .each axle, a draft tongue for leach axle extending forwardly thereof, means universally pivoting the forward end vof each draft tongueto said frame to provide for ,independentlangular movementof the axles relative to .one another, .a v,pair ofmspaced forevandaft beams spanning said axles, means universally pivoting the end portions of said beams to the respective axles, said means constructed and arranged to permit movement of said end portions relative to said axles in a direction transverse to said axles, two pairs of spaced guide members, one pair on each side of said frame extending downwardly on opposite sides of the central portions of the respective beams whereby each beam is disposed between a pair of said guide members, pivot means associated with each beam and cooperating to form a universal pivot for each beam, said pivot means and guide member being constructed to permit up and down movement of the beam between said guide members while maintaining the pivotal mounting of the beam relative thereto, and yieldable means interposed between said frame and beams and supporting said frame thereon.

3. In a tandem trailer assembly, an elongate frame, two tandem axles spaced longitudinally of said frame and providing a forward and a rear axle, two pairs of wheels, one pair on each axle, a draft tongue for each axle extending forwardly thereof, means universally pivoting the forward end of each draft tongue to said frame to provide independent angular movement of the axles relative to one another, a pair of spaced fore-and-aft beams spanning said axles, means universally pivoting the end portions of said beams to the respective axles, said means constructed and arranged to permit movement of said end portions relative to said axle in a direction transverse to said axle, two pairs of spaced guide members, one on each side of said frame and connected therewith, the respective guide members extending downwardly on opposite sides of the respective beams whereby each beam is disposed between a pair of guide members, inwardly concave and vertically elongated arcuate bearing surfaces on those sides of the guides' confronting the beams, convex bearing members mounted on the sides of the beams and turnable about a vertical axis between the guides while also slidable up and down to thus permit up and down movement of the beams between the guides, bearing means connecting each of said bearing members with their respective beams so that the beams are pivotal with respect to the bearing members about a horizontal axis intersecting said vertical axis at right angles, and resilient means interposed between said frame and beams and supporting the frame on the beams.

4. A tandem trailer assembly as in claim 3 wherein said resilient means comprises coil springs in compression.

5. A trailer assembly as in claim 3 wherein each said bearing means comprises a cylindrical boss projecting 10 from the beam and received in a rotatable fit in a mating socket formed in the bearing member.

6. In a tandem trailer assembly, an elongate frame, two tandem axles spaced longitudinally of said frame, two pairs of wheels, one pair on each axle, draft means associated with each axle and universally pivoting the axles to the frame for independent angular movement relative to one another, a pair of spaced beams transversely spanning said axles, means universally pivoting the end portions of said beams to the respective axles, said means constructed and arranged to permit movement of said end portions relative to said axles in a direction transverse to said axles, resilient means interposed between the centers of said beams and said frame and transmitting the weight of the frame to the beam, and connecting means between said frame and said beams and universally pivoting said beams relative to the frame, said connecting means including rigid guide members positioned on opposite sides ofsaid beams in bearing contact therewith and operable to transmit loads imposed on the beams in directions transverse to the frame directly to the frame without imposing side stress on said resilient means.

7. In a tandem trailer assembly, an elongate frame, two tandem axles spaced longitudinally of the frame, two pairs of wheels, one pair on each axle, draft means associated with each axle and universally pivoting the axle to the frame for independent angular movement relative to one another, a pair of spaced beams transversely spanning said axles, means universally pivoting the end portions of the beams to the respective axles while permitting movement of said end portions relative to said axles in a direction transverse to said axles, spring elements interposed between said beams and said frame to resiliently transmit the weight of the frame to said beams, and rigid means connected with the frame and disposed on opposite sides of each beam and having bearing contact with the beams for absorbing and transmitting directly to the frame,'independently of said spring elements, any side loads imposed on said beams tending to displace said beams relative to said frame.

References Cited in the tile of this patent UNITED STATES PATENTS 2,193,567 Pointer Mar. 12, 1940 2,493,004 Mackie Jan. 3, 1950 2,523,954 Jungwirth Sept.` 26, 1950 2,750,201 Hagedorn -..n June 12, 1956 

